It has been suggested that hepatitis C virus (HCV) strain variations could explain differing hepatocellular carcinoma (HCC) prevalences. However, few studies have examined the extent to which such variations occur in patients with HCC. Sera obtained between 1969-1981 from 91 HCC patients from Zambia, 35 from Uganda, and 27 from the United States were screened. A PCR-amplified 163-175 nucleotide segment of the 5'-noncoding region was sequenced by dsDNA cycle sequencing. Eight samples contained HCV-RNA (seven from Zambia; one from Uganda; none from the United States). Compared with the prototype strain HCV-1, at least four patterns of nucleotide variation were found. Variations of 0.5-2.3% were observed in this highly conserved virus gene segment. Some of these could be prevalent strain differences in Africa; three have been reported in >50% of HCV infections in Zaire and South Africa and two in >50% in Egypt. These data suggest HCC is not associated with a unique HCV strain, although critical mutations elsewhere in the HCV genome cannot be excluded. Serum samples collected in the 1970s from 25 HCC patients of Japanese descent from Hawaii and matched controls were tested for antibody to HCV and for the presence of HCV-RNA to determine whether HCV was associated with HCC in these patients as it is in Japan in the current decade. Anti- HCV was not detected in any HCC patients; HCV-RNA was detected in two. Although these results are not conclusive, they suggest that HCC in Hawaii was not highly associated with chronic HCV infection in the 1970s. (This may also have been true of HCC patients in Japan, since the evolution of the high prevalence of HCV-associated HCC in Japan today occurred during the past 25-30 years.)